Arabella Churchill, granddaughter of Sir Winston Churchill and a co-founder of the Glastonbury pop festival, who has died aged 58 of pancreatic cancer, meant so much to so many people over the years. A huge, indomitable personality who knew her own mind, she chose a very different path from the dictates of convention and her family background. She ploughed her own furrow and was proud of it.

Always intensely concerned for the underdog, she worked tirelessly at her Glastonbury-based Children's World charity, founded in 1981 to help children of all abilities but focusing in particular on those with special needs. She pioneered the annual Glastonbury children's festival, bringing alternative theatre acts to young and old audiences alike. As her friend and next-door neighbour for 20 years, I think I can speak for many in recalling in particular the Natural Magic Theatre Company, Parachute Theatre with their new slant on traditional puppetry - Punk and Judy - and the safe but near the knuckle Happy Sideshow.

Arabella started Children's World International in 1999, taking play equipment and basic things such as much-needed pens to the children of Kosovo and Albania, and then to post-tsunami Sri Lanka on an old doubledecker London bus. She also worked in Thailand and Banda Aceh, Indonesia. Her contribution included psychosocial work - morale-boosting get-togethers and workshops organised for children and their parents to focus on fun and games rather than the ordeal they had just faced. For such a small charity to survive for 20 years is a considerable achievement, and it is only thanks to her incredible commitment and sacrifice that it continues to exist.

But perhaps most of all Arabella is known for her role as co-founder of the Glastonbury festival in 1970 with Andrew Kerr and the farmer Michael Eavis. While the event is known primarily for its music, a key ingredient for long-time festivalgoers - and an often hidden surprise - is the outstanding array of theatre, cabaret and circus performances. Several fields dedicated to these arts were organised by Arabella herself. She found stunningly eccentric acts over the years, including the Cholmondeleys and Featherstonehaughs, Bill Bailey, the Stephen Frost Impro Allstars, BlackSkyWhite from Moscow, and many others.

The 1971 festival, which featured Hawkwind, Traffic, Melanie, David Bowie, Joan Baez and Fairport Convention, attracted 12,000 people. Revived as a three-day event in 1979, and latterly sponsored by the Guardian, it had grown to 153,000 visitors this year.

Born in London to Churchill's son Randolph and June Osborne, Arabella went to Fritham school for girls and then Ladymede school, near Aylesbury, Buckinghamshire. She worked at Lepra, the charity for leprosy sufferers, and then briefly at London Weekend Television before heading off to Glastonbury. She was debutante of the year in 1967 but by the mid-1970s, was living as a squatter in London and running a low-cost restaurant for fellow squatters.

"I'm immensely proud of my grandfather, and I hope he would be proud of me, but ... I was no good at being a Churchill," she said in a newspaper interview in June. "People never saw me for me. It doesn't do a lot for your confidence."

She continued to be a festival linchpin who, by dint of her enormous experience, developed a nose for entirely new, cutting-edge acts. A dynamic and decisive administrator with great attention to detail (she would always write personally to every single performer), she commanded loyalty and admiration from all who worked with her. She embraced Tibetan Buddhism through the teachings of Sogyal Rinpoche, author of The Tibetan Book of Living and Dying.

Knowing that she was dying, she wrote to friends: "Not really too worried about the actual dying bit, luckily - and please don't you be worried or sad either. Better this way for the soul than being run over by a big, red bus in a temper, completely unprepared!"

Her final days were spent at home in Glastonbury in a calm and peaceful atmosphere in harmony with her beliefs, surrounded by close friends and family.

She had been married to Haggis McLeod for 20 years and leaves a daughter, Jessica, aged 19, and a son, Jake Barton, aged 34, from her previous marriage to Jim Barton. On the day she died he was sentenced to three years in prison in Australia for his part in an ecstasy drug racket.